Electric discharge device having a low impedance at acoustic frequencies



June 13, 1961 G. J. M. AHSMANN ETAL 2,988,664

ELECTRIC DISCHARGE DEVICE HAVING A LOW IMPEDANCE AT ACOUSTIC FREQUENCIES8 Sheets-Sheet 1 Filed June 19, 1959 \NVENTORS GEIRARDUS JOSEPHUS MARIEAHSMANN HENDRIK JAN OSKAM AGENT June 1961 G. J. M. AHSMANN ETAL 2988,664

ELECTRIC DISCHARGE DEVICE HAVING A LOW IMPEDANCE AT ACOUSTIC FREQUENCIESFiled June 19, 1959 8 Sheets-Sheet 2 INVENTOR GERAR DUS JOSEPHUS MARIEAHSMANN HCNDRIK JAN OSKAM BY 4 ,e- 3.0%

AGENT G. J. M. AHSMANN ETAL 2,988,664 ELECTRIC DISCHARGE DEVICE HAVIJune 13, 1961 NG A LOW IMPEDANCE AT ACOUSTIC FREQUENCIES Filed June 19,1959 8 Sheets-Sheet 3 INVENTOR IE AHSMAN N GERARDUS JOSEPHUS MA? HENDRIKJAN OSKAM AG ENT J1me 1961 G J. M. AHSMANN ETAL 2 988,664

ELECTRIC DiSCI-IARGE DEVICE HAVING A LOW IMPEDANCE: AT ACOUSTICFREQUENCIES Filed June 19, 1959 8 Sheets-Sheet 4 \NVENTOR GERAR DUSJOSEPHUS MAEIE AHSMANN HENDRIK JAN OSKAM June 13, 1961 G. J. M. AHSMANNET AL 2,988,654

ELECTRIC DISCHARGE DEVICE HAVING A LOW IMPEDANCE AT ACOUSTIC FREQUENCIESFiled June 19, 1959 8 Sheets-Sheet 5 iNVENTOR GERARDUS JosEPHus MARIEAHSMANN HENDRIK JAN osKAM BY I 2 E L? AGENT 2,988,664 E DEVICE HAVING ALOW IMPEDANCE 8 Sheets-Sheet 6 June 1961 G. J. M. AHSMANN ETAL ELECTRICDISCHARG AT ACOUSTIC FREQUENCIES Flled June 19, 1959 le-i AGENT June 13,1961 G. J. M. AHSMANN ET AL 2,988,664

ELECTRIC DISCHARGE DEVICE HAVING A LOW IMPEDANCE AT ACOUSTIC FREQUENCIESFiled June 19, 1959 8 Sheets-Sheet '7 iCXJO mooo NVENTOR GERAR DUSJOSEPHUS MARIE AHSMANN HENDRIK JAN OSKAM June 13, 1961 G. .1. M. AHSMANNET AL 2,988,664

ELECTRIC DISCHARGE DEVICE HAVING A LOW IMPEDANCE I AT ACOUSTICFREQUENCIES Y 8 Sheets-Sheet 8 Filed June 19, 1959 GERARDUS JOSEPHUSMARE AHSMANN HCNDRIK JAN OSKAM United States Patent 2,988,664 ELECTRICDISCHARGE DEVICE HAVING A LOW IMPEDANCE AT ACOUSTIC FREQUENCIES GerardusJosephus Marie Ahsmann, Eindhoven, Netherlands, and Hendrik Jan Oskam,Minneapolis, Minn, assignors to North American Philips Company, Inc.,New York, N.Y., a corporation of Delaware Filed June 19, 1959, Ser. No.821,578 Claims priority, application Netherlands July 8, 19:8 Claims.(Cl. 313-226) Our invention relates to a gaseous electric dischargedevice employing a cold-cathode as an active element. More particularlythe invention relates to an electric discharge tube employing acold-cathode and a gas filling consisting essentially of a noble gas oflow atomic weight to which a noble gas of higher atomic weight is addedfor the purpose of decreasing the impedance at acoustic frequencies.

It is often desirable for gaseous discharge tubes in various circuits tohave as low an impedance as possible at acoustic frequencies. Thisapplies, for example to voltage stabilizers having gaseous dischargetubes since a voltage ripple of acoustic frequency must be smoother asmuch as a slow variation in voltage. Also, for example, in a telephoneexchange having switching tubes with or without an ignition electrodeand which convey currents of acoustic frequency, such tubes must have aslow an impedance as possible, since otherwise favourable proportioningof the various circuits is frequently impossible. In certain cases, thismay also apply to seriesdischarge tubes in which an anode coactsarbitrarily with one of a plurality of cathodes, which tubes areemployed in selecting or counting circuits.

An object of the present invention is to provide a tube having a coldcathode with a low acoustic impedance.

In a device according to the invention having a coldcathodegaseous-discharge tube as an active element, which tube has agas-filling substantially consisting of a noble gas of low atomicweight, to which a noble gas of higher atomic weight is added for thepurpose of decreasing the impedance at acoustic frequencies, the noblegas of the lower atomic weight is helium, neon, argon or krypton and thebalance of the mixture consists of neon and one or more of the gasesargon, krypton and xenon, or of argon and one or both of the gaseskrypton and xenon, or of krypton with or without xenon, or of xenononly. The expression active element does not include a rectifier tube.

In tubes employed in a device according to the invention, thecomposition of the rare gas is dependent upon the object aimed at. Thus,in a voltage stabilizer, in addition to the operating voltage and theslope of the static characteristic of the voltage-stabilizing tube, onlythe impedance is important and not the restoring time after theextinction of the discharge. On the other hand, in a telephone exchangein which telephone currents traverse gaseous discharge tubes, it is notonly the impedance of the discharge tubes which is important in additionto the static characteristic and the breakdown voltage, but also therestoring time after the extinction of the discharge. According to theinvention, it has been found that, in order to obtain a short restoringtime, the amount of the heavy rare gas must frequently be chosen largerthan in other mixtures of lower impedance, since small amounts of heavyrare gases in the above-mentioned combinations result in the restoringtime being lengthened, except in the case of He as the main gas.

Thus, in a tube according to the invention, which contains Ar and Kr,the percentage of Kr must lie upwards of lest the restoring time islonger than in pure Ar.

The impedance-reducing effect of the admixtures may Patented June 13,1961 ICC be explained with the aid of considerations regarding chargetransfer phenomena between ions and atoms.

In a discharge in a mixture of gases which substantially consists of alight rare gas and a small amount of a heavy rare gas, preferably theions of the admixture are produced. This is attributable to the factthat the atoms of the heavy gas have an ionization voltage lower thanthat of the light gas and also a greater probability of ionization.However, in certain cases, ions of the light rare gas are also produced.The ions of the light main gas, upon impact with atoms of the admixturehaving a lower ionization voltage, can still transfer the charge tothem. The ions of the admixture, because of the low concentration of theatoms thereof, impact so little with atoms of the same or lowerionization voltages that they cannot substantially transfer their chargeand hence retain their full velocity. On the other hand, in a pure raregas, new ions or ions produced by transfer of charge constantly impactwith neutral atoms, whereby each time the charge is transferred so thatthe velocity on the average remains low. Consequently, the result of theprocesses is that in a rare gas containing a heavier gas admixture, themobility of the ions in the dark room of Crookes, which is substantiallya measure of the impedance, is considerably greater than in the case ofpure rare gas. As a result thereof, the impedance of the mixture islower because of its greater mobility of the ions than in the case ofpure rare gas.

The invention will be described with reference to the accompanyingdrawings, in which:

FIGS. 1 and 2 show tubes with which measurements were effected;

FIG. 3 shows a relay tube on which measurements have been carried out;

FIG. 4 shows a voltage-stabilizing tube on which measurements have beencarried out;

FIGS. 5 to 11 show graphs of results obtained in the measurements.

Referring now to FIG. 1, in a glass bulb 1 there are arranged twocircular molybdenum plates 2 and 3 each of 15 mms. in diameter with adistance of a few millimetres between them. Connected to the bulb 1 is ahorizontal tube 4 to which a plurality of small glass vessels 5, eachclosed by a spherical capillary tube 6, is connected. The sphericalcapillary tubes 6 may be opened by means of a steel pellet 7. Each glassvessel 5 is filled with an exactly proportioned amount of rare gas or amixture of rare gases. The bulb 1 is also filled with a pure rare gas.At a given current strength between the electrodes 2 and 3, theimpedance of the discharge space at several frequencies is now measuredsuccessively in the pure rare gas and after certain amounts of heavyrare gas have been added thereto from the vessels 5. The pressuresprevailing in the vessels 5 must be equal to the pressure in the bulb 1,since otherwise variations in pressure may occur and impede properjudgement of the results.

In FIG. 2, the cathode is constituted by a molybdenum cylinder having adiameter of 12 mms. and a length of 20 mms., the centrally-arrangedanode being a molybdenum rod having a diameter of 2 mms. and a length of25 mms.

In FIG. 3, the bulb of the switching tube is indicated by 10. A nickelcathode 12 and a nickel anode 13 are pinched between two mica plates 11.The cathode is activated with a mixture of alkaline-earth oxides '14.The anode and the cathode each have a width of 4.5 mms. and a length atright angles to the plane of drawing of 8.5 mms., while the spacingbetween them is 2.75 mms. Arranged at each end of the cathode, at adistance of 0.2 mm. thereof, there is arranged an auxiliary anode wire15 having a thickness of 0.3 mm. The electrodes are connected to pins 16by means of supporting wires.

FIG. 4 is a perspective view, partly open, of the bulb 17 of astabilizing tube, the base of which contains a plurality of pins 18. Twoslightly-curved molybdenum plates 19 and 20 are fitted on the pins 18with a spacing of 6 mms. The plates measure 40 x 30 mms. and have athickness of 0.2 mm. each. The pressure is 7 mms. of mercury.

In FIGS. 5 and 6, the impedance Z in ohms of the tube shown in FIG. 1 isplotted in the complex plane, that is to say, the real part of theimpedance X along the horizontal axis and the imaginary part Y along thevertical axis wherein Z=X+jY. FIG. 5 shows the results measured for acurrent strength of 2 ma. and FIG. 6 for a current strength of 3.5 ma.,wherein the line A applies to pure argon, the line B toargon and 5% ofxenon, the line C to argon and of xenon, and the line D to argon and ofxenon. The distance between the electrodes is 8 ms. and the pressure is8 mms. of mercury. The numerals specified indicate the frequencies inc./s. at which the measurements were carried out.

FIGS. 5 and 6 clearly show that the addition of 5% of xenon to argonconsiderably decreases the impedance at both 2 ma. and 3.5 ma. If thepercentage of xenon is increased to 10% or 20%, the imaginary part Y ofthe impedance further slightly decreases and from the curves an increaseof the real part seems apparent. However, the latter phenomenon is theresult of an additional effect which may be prevented by slightlyincreasing the total pressure, since as a result of the admixture, thenormal current density varies slightly so that at this current strengthand pressure the discharge can start to burn slightly abnormally and, asappears from a comparison of FIGS. 5 and 6, the real part of theimpedance with abnormal burning (3.5 ma.) is larger than in the normalrange (2 ma.).

The choice of the percentage of xenon in a given tube is dependent interalia upon the desired restoring time which for higher percentages ofXenon may lie below that of pure argon.

FIGS. 7 and 8 show the results of a series of measurements withargon-krypton mixtures in a tube as shown in FIG. 1, that is to say,again with a distance of 8 mms. between the electrodes and a pressurelikewise of 8 mms. mercury column, FIG. 7 applying to a current strengthof 2.5 ma. and FIG. 8 applying to a current strength of 3 ma. Curve Erelates to pure argon, curve F to argon and 12.25% of krypton, and curveG to argon and 24% of krypton. From the specified values it clearlyfollows that the material decrease in impedance by addition of 12.25% ofkrypton is retained, whereas if the percentage of krypton is increasedto 24%, a small increase of the real part of the impedance attributableto additional effects as in the case of argon-xenon is obtained.

FIGS. 9 and 10 show the results of measurements carried out with thetube of FIG. 2 in neon-krypton mixtures at current intensities of 6ma.and 11 ma. Curve H relates to 100% of neon, curve I to neon and 5% ofkrypton, and curve K to neon and 17% of krypton. In connection withthese figures the following remarks may be made. By the addition of anamount of krypton to neon, the normal current density considerablydecreases. The inductance of a gaseous discharge is then inverselyproportional to pressure. If, for example, with 5% of krypton, thecurrent density is again brought to the value of that of pure neon byincreasing the pressure, the line I would lie even lower, but especiallymore to the left, since the real part is smaller in the normal range ofthe discharge. Otherwise, in designing a tube, the current densitychosen greatly depends upon the life desired, especially if incontradis'tinction to the measuring tube, use is made of an activatedcathode.

In connection with the foregoing it may be mentioned that the eifect ofthe addition of krypton to neon upon the impedance is much stronger thanthe effect of the addition of krypton to Xenon or argon. Nevertheless astrong decrease in impedance is not limited to neonkrypton mixtures,since helium upon addition of even small amounts of neon up to anoptimum at about 5% also provides a greatly decreased impedance. Inaddition, this mixture has still other diifering properties, sinceprecisely at very low percentages of neon an appreciable shorteninginstead of a lengthening of the restoring time occurs.

With regard to the tube shown in FIG. 3, it is to be noted thatmeasurements have revealed that in this tube also an impedance-reducinginfluence of krypton upon argon occurs. In connection with the desireddecrease in restoring time, the optimum percentage of krypton liesbetween 15% .and 20%.

FIG. 11 shows the results of measurements carried out with thevoltage-stabilizer tube of FIG. 4, in which line L applies to a currentstrength of 7.5 ma. with of argon and line M relates to a filling ofargon and 5% of xenon at the same current strength. Lines N and P applyto the same fillings, but at 10 ma. The slope of the staticcharacteristic of the tube in the region of from 1 to 15 ma. was, on theaverage, not more than 20 ohms.

While we have thus described our invention with specific examples andapplications, we do not wish to limit thereto as other modifications andapplications will be readily apparent to those skilled in the artWithout departing from the spirit and scope of the invention as definedin the appended claims.

What we claim is:

1. In an electrical system of the type including a source of electricalsignals and utilization means therefor, an electron discharge deviceinterconnecting said source and utilization means, said devicecomprising an envelope, a cold cathode, an anode, a first noble gasselected from the group consisting of helium, neon, argon, and krypton,and a second noble gas for reducing the impedance of said device atacoustic frequencies admixed with said first noble gas, said secondnoble gas having an atomic Weight greater than that of said first noblegas and argon.

2. An electron discharge device as claimed in claim 1 in which thesecond noble gas is xenon.

3. An electron discharge device as claimed in claim 1 in which the firstnoble gas is argon which is admixed with 15 to 20% of krypton.

4. An electron discharge device as claimed in claim 1 in which the firstnoble gas is neon which is admixed with 15 to 20% of krypton.

5. An electron discharge device as claimed in claim 1 in which the firstnoble gas is argon which is admixed with about 5 to 20% of xenon.

References (Iited in the file of this patent UNITED STATES PATENTS1,949,069 Balcar Feb. 27, 1934 2,436,835 Stutsman Mar. '2, 19482,688,708 Charlotte Sept. 7, 1954 2,763,806 Anderson Sept. 18, 19562,796,558 Koehler June 18', 1957

